Disc drives are data storage devices used to store and retrieve digital user data in a fast and efficient manner. A typical disc drive stores such data on a number of magnetic recording discs which are rotated at a constant high speed. An actuator controllably moves a corresponding number of data transducing heads to access data stored in tracks defined on the disc surfaces.
Servo data are written to the discs during disc drive manufacturing to define the tracks and to provide head positional information to a closed loop servo control circuit. The servo circuit applies current to an actuator motor to move the heads across the disc surfaces. In an embedded servo scheme, the servo data are arranged in servo sector patterns. The servo sectors are angularly spaced apart and interspersed with user data sectors to which user data are stored.
A continuing trend in the disc drive industry is to provide disc drives with ever increasing data storage and transfer rate capacities. As track densities continue to increase, it becomes increasingly important to provide servo circuits that are capable of accurately positioning the heads during seeks and track following modes of operation. Various gains of the servo circuit are typically selected to achieve a certain control response for the servo circuit; however, changes in environmental conditions and other factors tend to affect the characteristics of the actuator motor and servo circuit during operation.
Accordingly, there is a continuing need for improvements in the art whereby the robustness of disc drive servo systems can be enhanced over a broader range of environmental conditions.